The invention relates to a membrane module of an installation for membrane separation of material mixtures comprising one or more tube membranes, a process for their manufacture by extrusion of synthetic material as well as applications of the membrane module.
Such membrane modules are known as structural elements in cross current filtration plants. They comprise mostly a plurality of tube membranes acting as filters. The tube membranes are designed as porous tubes either themselves designed as membrane filters or carrying filtration membranes of organic or inorganic materials on their surface. Tube membranes comprising interior or exterior membranes, are known. Their inside diameters range from some decimillimeters to about 100 millimeters.
In order to attain acceptable construction lengths of the membrane modules, combined with a useful filtration output, a small or larger number of straight tube membranes are installed in a straight jacket tube. This module tube has a combined entry and exit for all tube membranes for the medium to be filtered as a retentate and one or two exits for a filtrate as a permeate.
Membrane modules designed as so-called coil modules are also known. In this context cloth-like filter membranes are wound into an elongate roll in which the flow-through of the retentate and the drainage of the permeate is made possible by co-wound thin elastic spacers or nets. Coil modules of this design are very reasonably priced having regard to their filtration performance. However, because of their tendency to clog they are unsuitable for the separation of material mixtures having a high solids content. In contrast to this, with tube membranes having an inside diameter of some millimeters (a plurality of millimeters) even material mixtures having a high solids content such as pressed fruit juices, for example, can be processed without risk of clogging.
As the specific filtration output, in relation to the surface area, of known tube membranes of polysulphone or PDVF is relatively low, a number of modules, each comprising e.g. 19 tube membranes of 3 m length each, are interconnected in one installation in series and also in parallel in order to attain higher, economically acceptable filtration outputs.
If the number of the modules connected in series is high, up to 16 modules per series are known, the latter are interconnected by way of 180 degree pipe bends. If the group comprises as few as 5 series or passes switched simultaneously in parallel, 80 modules have to be provided in as compact a single unit as possible in order to attain a membrane filter surface area of about 180 m.sup.2. The individual modules are for this purpose mounted on support arms on racks and the numerous connections on the retentate side and the permeate side are brought about. This entails the following problems:
4 tube connections and two to three supports on support arms are required per membrane module. In an installation having 80 modules, these connections and supports result in 80 connecting bends, 85 hose connections and 320 connecting points, they further result in high installation costs thus reducing the cost efficiency of the plant. PA1 Separating membranes have only a limited useful life. The membrane modules are thus parts subjected to wear and tear, having to be replaced at certain time intervals.
The efforts for assembly and disassembly as well as for the complex construction are thus enormous for this design.